Document copiers



July 13, 1965 G. H. ROBINSON DOCUMENT COPIERS Filed Oct. 9, 1962 GENE H. ROBINSON IN VEN TOR.

ATTORNEYS United States Patent 3,194,131 DQCUMENT CGPEERS Gene H. Robinson, Rochester, assignor to Eastman This invention relates to document copiers and particularly to methods of and apparatus for holding the document to be reproduced.

It is essential in some forms of photocopying devices that the document to be copied and a matrix or receiving sheet be held in intimate contact during a part of the reproduction process. Often, the surfaces on which these materials are to be held are curved, which increases the difficulty of manipulating the sheets. Further, the handling problem with some documents to be reproduced, such as trucking way-bills, is aggravated by a curl imparted to them by the tubular containers within which they are transported.

Mechanical devices for overcoming these problems have been proposed; however, they are all somewhat difiicult to use and expensive to manufacture. Electrostatic apparatus for holding the documents has been proposed to overcome the disadvantages of mechanical devices. For example, see Gage US. Patent 2,742,814,

'Oughton, US. Patent 2,543,051, and 7 of copending application, U.S. Ser. No. 25,108, filed April 27, 1960, by James G. Jarvis. ln'the latter case, a xerothermographic recording layer and a document are held in intimate contact by electrostatic forces to insure against unsharpness and loss of density in reproduction. An insulator-covered conductor is corona charged, the document is applied and covered with a xerothermO- graphic recording sheet and this sheet is then charged with a corona of a polarity opposite to that first used. The charge on the surface of the xcrothermographic layer being opposite to that which resides on the insulating surface of the supporting plate creates an electrical held and force which tend to compress the sandwich, thereby creating an intimate contact between the two layers. The document could, alternatively, be placed on the supporting plate before the first charging operation. in such an arrangement, two sheets are held to a supporting surface 'by the use of two charging operations. No mechanical holding devices are required.

These electrostatic systems are simple and less expensive than the mechanical devices, but they also have certain disadvantages. For example, these electrostatic systemsrequire ion sources, such as needles, wires, or conducting rollers, which externally protrude, are often delicate, and which require a certain amount of maintenance. Further, these systems present a possibility of shock hazard to the operator. In operating these systems the step of charging the insulating layer to hold the document is a separate step which must be taken after one document has been reproduced and before the next document is fed into the copier. These disadvantages are overcome by the present invention.

It is an object of the invention to provide a method of and an apparatus for electrostatically holding documents in a copier which eliminates the possibility of shock hazard.

It is a further object to provide an electrostatic holding for to the insulator.

apparatus which does not depend upon nor require external ion sources, such as needles, wires, or conducting rollers.

it is another object to provide a method and apparatus for electrostatically holding documents in a copier which does not require a separate step in the reproduction process, but which can be done while simultaneously reroducing previous documents.

These and other objects and advantages of the present invention are accomplished by the following method and apparatus. present invention the layer which is to hold the document is an electrically insulating layer which is electrostatically charged simultaneously with any of the steps of the reproduction processof a preceding document. Preferably this simultaneous charging step is performed in such a manner as to eliminate any possibility of shock hazard. This is accomplished by applying a charge of one polarity to alternate increments of relatively small area and applying a charge of opposite polarity to the remaining increments of relatively small area. '5 he apparatus according to the invention consists of a grounded conducting plate overlayed with an insulating layer. This is the document receiving and holding plate. A facing electrode is positioned adjacent this plate and a EGGS-volt potential is applied to the electrode. A gaseous breakdown occurs in the air gap allowing charge trans- For convenience the charging may be considered as a hybrid of field charging and corona charging; but the invention does not depend on any particular theory. The resulting charge is sufficient to hold documents to the insulating layer by electrostatic forces.

These and other objects and advantages will be more fully understood from the following description when read in connection with the accompanying drawing in which:

FIG. 1 is a partly schematic cross-sectional view of one embodiment of the present invention;

FIG. 2 is a partly schematic cross-sectional view of the preferred embodiment of the present invention; and,

FIG. 3 is a partly schematic plan view of the preferred form ofthe electrodes of the present invention.

The present invention will be described with reference to a photocopier of the type having a curved transparent exposing platen and a curved cover which is hinged to fit directly over the platen.

FIG. 1 shows a transparent glass platen in over which the cover 111 is positioned during the reproduction process. In the normal operation of the copier, one or more documents 12 to be copied and a matrix 13 are held between the cover ill and the platen ill.

Howeven'the manipulation of the matrix and of a plurality of documents, when placing these sheets between the curved surfaces (sometimes curved opposite to the curl in the documents) is an almost impossible task for the operator without the aid of some auxiliary device. By means of the present invention, now to be described, these difficulties have been obviated.

As shown in FIG. 1, the existing cover 11 of the machine is underlayed with a grounded metal electrode 14 which in turn is underlayed with an insulator 15, such as polyethylene terephthalate having athickness of uses inch, to form a cover assembly to.

The existing glass platen ill is covered with a transparent electrode 17. The glass platen It! and the transin the preferred method according to the parent electrode 1'7 comprise the exposing surface 19. The electrode 17 may consist of glass having a thin, transparent, conducting film of tin oxide thereon. The electrode 17 consists of, in the preferred embodiment, a set of two interdigital electrodes connected to a power supply 21, as described in more detail below with reference to FIG. 3.

In operating this embodiment of the present invention, the cover assembly 16 is closed so that it is positioned adjacent the exposing surface 19. The documents 12 and the matrix 13 are not present at this time. A 2000-volt potential is applied from the power supply 21 to the transparent electrode 17 for about six seconds with the electrode 14 grounded. A gaseous breakdown occurs in the air gap between the insulator 15 and the transparent electrode 17, which allows charge transfer to the insulator. This transferred charge, now residing on the insulator 15, is sufiicient to hold the documents 12 by electrostatic forces against both the curvature of the cover assembly is; and the curl in the original documents 12.

The operators only function after placing the document on the insulator I is to insert the matrix 13 in the normal manner and close the cover assembly 16. The matrix 13 is then exposed and processed in the usual manner. The handling of subsequent documents need not require a separate closing of the cover assembly to for charging purposes, as a satisfactory charge level can be maintained by charging during the exposing step of the immediately preceding matrix. Of course, the cover assembly must be opened for removing and inserting documents and matrices and the cover assembly is closed after insertion of a document and a matrix. But, when reproducing a series of documents one after the other, the separate charging step used with the first document to be reproduced, need not be carried out for any of the subsequent documents, i.e., there need not be a separate closing of the cover assembly for charging purposes, with neither document nor matrix present, since the insulator can be charged to hold the next document, during the step of exposing the preceding matrix.

FIG. 2 shows the preferred embodiment of the present invention. As shown, the structure is essentially identical to the structure of FIG. 1, except that the original cover plate and transparent glass platen have been omitted. The cover assembly in this embodiment consists of a grounded metal electrode 31 and an insulating layer 32. The transparent electrode 33 is the exposing surface. The metal electrode 31 may take the place of the previously existing cover without any possibility of shock hazard since it is grounded. The transparent electrode 33 may take the place of the previously existing exposing surface as it can be made as structurally strong as required. It may consist for example, of glass with a thin, transparent, conducting coating 34 of tin oxide on the outer surface. The electrically conducting coating 34 of the transparent electrode 33 consists of, in the preferred embodiment, a set of two interdigital electrodes connected to a power supply 21, as described in more detail below, with reference to FIG. 3.

FIG. 3 shows the preferred construction of the charging electrode (17 in FIG. 1 and 34 in FIG. 2) in which the possibility of getting a shock has been eliminated. As shown in FIG. 3 the charging electrode an is formed as a set of two interdigital electrodes 41 and 42. The electrodes 41 and 42 are provided with a plurality of fingers 43 and 44- respectively, which are preferably about /2 inch wide. The electrodes 41 and 42 are respectively connected through the switches 4-7 and 48 to positive and negative power supplies and 46, see also FIGS. 1 and. 2. The connections 54 and in FIGS. 1 and 2, respectively, are to one of the two interdigital electrodes 41 and 42 and the connections 56 and 52, in FIGS. 1 and 2 respectively, are to the other of the two interdigital electrodes 41 and 42. Electrostatic holding forces are the same as before because any small area of the document is subjected to exactly the same force as with one polarity charging. However, the possibility of getting a shock from the insulator 15 is eliminated because a conductor placed on the insulator is actually on a surface of neutral potential due to the balance of positive and negative charges. Charging times are of the order of 6 seconds when using a -megohm resistor in the power supply lead. It is to be noted that other electrode arrangements may be used. For example, a matrix or grid arrange ment could be used wherein adjacent but spaced squares of the electrodes are of opposite polarity. The only requirement is that the insulating layer is charged in such a manner that the surface potential integrates to substantially zero, due to the balance of positive and negative charges.

Of course a different shock hazard could exist if the operator were to accidentally touch the high voltage output of the power supply, which is capable of delivering l milliainpere at 2000 volts. By introducing a 100-megohm resistor into the high voltage lead, the current flow at 2000 volts can be reduced to a harmless 0.003 milliarnpere, which is still adequate for electrostatic charging.

While the preferred embodiments of the present invention have been described in detail, it is to be noted that the preesnt invention is not limited to such embodiments. For example, the present invention is useful in any application Where a conducting sheet is to be attached to an insulating surface.

Having described the preferred embodiments of my invention, I wish to point out that it is not limited to this specific structure, but is of the scope of the appended claims.

I claim:

I. An electrostatic document holding apparatus comprising a first electrode plate consisting of a set of interdigital electrodes, a grounded second electrode plate removably positioned in contiguous facing relationship to said first plate and having a coating of non-photoconductive insulating material on the side facing said first electrode plate, and means for energizing adjacent electrode digits of said first electrode plate to electric potentials of opposite polarity, said potentials being of a sufficiently high value to cause ionization of the air between said two plates.

2. An electrostatic copy holding apparatus for use in a document copier comprising a transparent electrode exposing plate, said transparent electrode consisting of a set of interdigital electrodes, a cover removably positioned in contiguous facing relationship to said exposing plate and consisting of a grounded electrode plate having a coating of non-photoconducting insulating material on the side facing said exposing plate, and means for energizing adjacent electrode digits to electric potentials of opposite polarity and of a value sufiiciently high to cause ionization of the air in the gap between said exposing plate and said cover.

3. An electrostatic copy holding apparatus for use in a document copier having a. concentrically curved transparent exposing plate and a readily removable cover comprising a grounded electrode plate underlying said cover, a non-photoconductive insulating coating underlying said grounded electrode plate, a transparent electrode coating consisting of a set of interdigital electrodes overlying said transparent exposing plate, and means for energizing adjacent electrode digits of said transparent electrode to electric potentials of opposite polarity sufiicient to ionize the air in the gap between said transparent electrode and said insulating coating when said cover is closed, to electrostatically charge said insulating coating.

A method of electrostatically charging one surface of a non-photoconductive, insulating plate to prepare it to support an electrically conductive document by electrostatic forces comprising the steps of electrostatically charging alternate increments of relatively small area arranged in a substantially uniform pattern on said insulating plate with electrical charges of one polarity and electrostatically charging the remaining alternate increments of said pattern with electrical charges of the opposite polarity, and placing said electrically conductive document in contiguous face-to-face relationship with said electrostatically charged plate whereby the possibility of shock hazard is reduced.

References Qitcd toy the Examiner UNETED STATES PATENTS Oughton et a1 951.7 X Gage 951.7 X Ebert 951.7 X Dessauer 951.7 X Bixby 951.7 X Sehwertz 951.7 X

10 EVUN C. ELUNK, Primary Examiner. 

4. A METHOD OF ELECTROSTATICALLY CHARGING ONE SURFACE OF A NON-PHOTOCONDUCTIVE, INSULATING PLATGE TO PREPARE IT TO SUPPORT AN ELECTRICALLY CONDUCTIVE DOCUMENT BY ELECTROSTATIC FORCES COMPRISING THE STEPS OF ELECTROSTATICALLY CHARGING ALTERNATE INCREMENTS OF RELATIVELY SMALL AREA ARRANGED IN A SUBSTANTIALLY UNIFORM PATTERN ON SAID INSULATING PLATE WITH ELECTRICAL CHARGES OF ONE POLARITY AND ELECTROSTATICALLY CHARGING THE REMAINING ALTERNATE INCREMENTS OF SAID PATTERN WITH ELECTRICAL CHARGES OF THE OPPOSITE POLARITY, AND PLACING SAID ELECTRICALLY CONDUCTIVE DOCUMENT IN CONTIGUOUS FACE-TO-FACE RELATIONSHIP WITH SAID ELECTROSTATICALLY CHARGED PLATE WHEREBY THE POSSIBILITY OF SHOCK HAZARD IS REDUCED. 